Сам разобрался, помогли вот такие правила:
/ip firewall nat
chain=dstnat action=netmap to-addresses=192.168.0.31 to-ports=80 protocol=tcp dst-address=Б.Б.Б.Б dst-port=99
chain=srcnat action=masquerade to-addresses=192.168.0.31 src-address=192.168.0.0/16 dst-address=192.168.0.31
out-interface=bridge-local
/ip firewall mangle
chain=forward action=mark-connection new-connection-mark=t31 passthrough=no src-address=!192.168.0.0/16 dst-address=192.168.0.31
chain=prerouting action=mark-routing new-routing-mark=Б passthrough=no src-address=192.168.0.31 connection-mark=t31
/ip route
A S ;;; Routing Mark - Б 0.0.0.0/0 Б.Б.Б.Б 1
Может кому пригодиться!
